Axial flow fan



June 5, 1951 Filed May '7, 1946 A. E.'CRlQUl AXIAL FLOW FAN 5 Sheets-Sheet l ATTORN EY I June 5, 1951 Filed May 7, i946 A. E. cRlQul 2,555,576

AXIAL FLOW FAN 3 Sheets-Sheet 2 INVENTOR June 5, 1951 A. E. cRlQUl 2,555,576

4 AXIAL FLOW FAN Filed May '7, 1946 3 Sheets-Sheet 5 INVENTOR l Alberi; E. C/'qu/ ATTORNEYS Patented June 5, 1951` AXIAL FLOW FAN Albert E. Criqui, Kenmore, N. Y., assignor to Bulfalo Forge Company, BuHalo, N. Y.

Application May 7, 1946, Serial No. 667,927

tion of the outer diameter of the wheel, and the inner cylinder is usually of substantially the same diameter as the hub diameter. Under these conditions, when the air stream leaves the outer end of the cylinder, a central reduced pressure area is created in the stream, thereby causing turbulence and eddy currents which greatly reduce the efficiency of the fan. This condition can be remedied by providing suitable streamlining eX- tending from the downstream end of the inner cylinder in the nature of a tailpiece for occupying the reduced air pressure area of the stream. By

the use of such a tailpiece, the ow of the air stream may be made to converge within the -bounds thereof without serious eddying or turbulence. However, such a tailpiece cannot be used when the velocity of the air stream must be distributed in a short distance from the fan. When attempts are made to overcome this drawback by using a shorter tailpiece, the boundary layer of air builds up and the air stream tends to leave the receding surface of the tailpiece. Furthermore, an undesirable boundary layer condition also usually exists at the convex sides of the diffuser vanes. For these reasons, means must be employed to control boundary layer` and thereby cause the stream to follow the Oblique surfaces over which it is to pass, without creating turbulence and eddy currents.

The principal object of my invention has been `to provide means for removing the boundary layer and thereby causing the stream of air passing through an axial flow fan to remain in contact with the oblique surfaces thereof.

Another object has been t provide means for improving the efficiency of axial flow fans which shall be self-contained and adapted for use upon existing fans without re-design thereof or lengthy interruption of service during the installation.

Moreover, my invention provides means for im- `proving the flow of air over the straightening or diffuser vanes of axial flow fans by causing the stream to remain in contact with the back surface of the curved portions of the vanes,

Furthermore, the invention has for an object to provide means for creating uniform velocity of the air stream at the fan outlet so that when used in connection with heating or cooling coils, maximum efficiency may be obtained.

The above objects and advantages have been accomplished by the device shown in the accompanying drawings, of which:

Fig. 1 is a longitudinal sectional view of an axial flow fan embodying one form of my invention;

Fig. 2 is a similar view of a fan embodying another form of the invention and illustrates it as applied to diffuser Vanes;

Fig. 3 is a fragmentary diagrammatic View of another form of the invention also applied to diffuser vanes;

Fig. 4 is a fragmentary diagrammatic sectional view of my invention as applied to an air duct having a flaring funnel-shaped outlet; and

Fig. 5 is a fragmentary sectional view of a fan equipped with another embodiment of my invention.

In carrying out my invention, means are employed to cause air to follow contours which have oblique or curved surfaces which are directed away from the course of the stream to a degree greater than normal, whereby the axial distance required for desirable flow of air in an axial flow fan can be made so short as to adapt my invention to many practical uses. It is well known that the practice of boundary layer control can be effected in two ways. One is to introduce supplemental air to the stream near the point where separation would take place so that the flow will continue to follow the surface without separating from it. A second method is to draw the boundary layer off at a point where separation would normally occur. In carrying out my invention, the stagnant air of the boundary layer is removed and thereby prevented from building up to a critical point with the result that the main air stream is drawn down towards the surface. In order to control this undesirable boundary layer, I utilize the pressure differences which exist between the air stream and the area of reduced pressure at the center of the stream.

Referring now to the form of device shown in Fig. 1, the fan comprises a wheel I having blades I I and mounted for rotation within an outer cylinder or duct I2. As shown in this figure, the means for impelling the fan is an electric motor I3 which is mounted within an inner cylinder I4. As is customary, this cylinder is maintained in position by means of the straightening 0r diffuser 3 vanes I5 which are secured along their inner edges to the inner cylinder and along their outer edges to the duct I2. Air being forced through the duct by the fan wheel follows the course indicated by the arrows. The air stream in passing through the fan wheel is given a helical path which is straightened out by passage over the straightening or diifuser vanes I5, whereby the air leaves the downstream edge of the vanes in a substantially true axial course. As the air stream passes the end of the inner cylinder I4, there is a tendency for it to continue in a straight course; and, since an area of reduced pressure will be formed immediately behind the inner cylinder, turbulence and eddy currents would ordinarily result. To avoid this condition and to cause a uniform distribution of the velocity of the stream, I provide a tailpiece i6 composed of a number of partially nested cone shape members 2B, 2l, 22, and 23 each having a surface obliquely arranged with respect to the normal air flow. The member is preferably secured to the downstream end of the inner cylinder I4 and the member 2l has its upstream end mounted within and in spaced relation with the rear end of the member 20, thus `providing a space t0. In like manner, the forward end of the member 22 is mounted within the downstream end of the member 2! and in spaced relation therewith thereby forming an annular opening 3|. An annular opening 32 is likewise formed between the members 22 and 23. The member 23'is formed with a central opening 33 at its downstream end. Suitable means (not shown) are provided for properly securing the members together.

VAs the .air stream passes over the downstream edge of the member 2li, it will cause air to be aspirated through the opening 30. This air is added to the air of the main stream which tends to draw the stream toward the tailpiece. Air passing openings 3l and 32 likewise causes supplemental air to be aspirated through these openings which causes the air stream to continue along thergeneral cuter surface of the tailpiece and to be drawn toward the center of the duct, thereby equalizing its velocity. When supplemental air is supplied to the air stream through the openings 30, 3l, and 32, an area of reduced pressure .is created within the tailpiece. Since the member 23 has a central opening 33, some air will be taken from the main stream to equalize the pressure within the tailpiece and to supply the additional air for passage out through the openings 35 to 32.

My invention can also be advantageously employed in the control of boundary layer occurring at the back convex sides of the diuser or straightening vanes of an axial flow fan as shown in Fig. 2. In this figure, the fan wheel 4o is mounted upon a suitable shaft 4l which is supported in bearings 42 carried by the inner cylin- A der 43 of the fan. This cylinder is maintained in spaced relation with the Vouter cylinder or duct 44 by 'means of the diffuser vanes 45. It will be seen that air coming from the fan wheel in a helical path will be projected against the inner curved surface of the vanes 45, but that there will be a tendency for the air to leave the back curved surfaces of the vanes, thereby causing boundary layer resulting in the creation of eddy currents and consequent loss of eiiciency. In applying my invention Vto this condition, I provide the inner cylinder with an opening or slot 45 located iinmediately behind each of the vanes on the convex sides thereoffwhereby air passing across the back Vof slots or apertures 1l).

pirated through the opening 46, thus drawing airY from the inside of the cylinder and introducing it into the stream at the point where separation would occur with the result that the air stream will closely follow the convex contour of the vane. Obviously, the inner cylinder 43 is closed at its forward end and open at its rear end whereby air will be drawn into the interior thereof for supply to and through the openings 46. In this form of invention, the fan is driven by an eX- ternal motor (not shown) through the medium of suitable belts 5t passing over a pulley 5I attached to the fan shaft and out through the inner cylinder 43 and the wall of the duct 44 through a fairing 52.

Another form of my invention as applied to diffuser vanes for causing the air to follow the rear convex surfaces thereof is shown in Fig. 3. In this form, each vane 53 is provided with a plurality of openings or perforations 54 whereby a portion of the air striking the concave surface of the vanes will pass through the openings and thus serve to supply the additional air needed to cause the stream to follow the rear convex surface of the vane.

Another form of device for carrying out my invention is shown in Fig. 4. As here illustrated, the air stream coming through the duct 55 by means ofthe fan 59 is caused to be diverged by passage through a aring funnel-shaped outlet 56 having walls obliquely arranged with respect to the air flow. This form of the invention is applicablefor use in connection with heating andvcooling coils; and in carrying it out, I provide an inner cone '6U within the funnel-shaped outlet. This cone 60 is formed in its oblique wall with a plurality of slots 6l forming tab members 62 which have their downstream edges 63 iiared outwardly as shown in the drawing. The outer layer of the air stream coming from the duct will pass between the cones 56 and 6B and supplemental air from the central portion of the stream will be caused to be aspirated through the slots 6l and therefore diverted from Vthe center toward the outside of the stream, thereby equalizing the velocity across Vthe area.

In the `form of invention shown diagrammatically in Fig. 5, the inner cylinder 65 is provided with a tailpiece 66 formed with a plurality A conduit 'Il extends into the tailpiece and has its outer endv connected to a source of vacuum whereby a reduced pressure is maintained within the tailpiece causing air to be drawn in through the slots 10 thus removing the boundary layer and distributing the air stream uniformly across the area of the duct.

While I have shown a number of illustrative uses of my invention, it is obvious that modications thereof may be made without departing from the spirit of the invention or the scope of the appended claims; and I do not, therefore, wish to be limited to the exact embodiments herein shown and described. Furthermore, while I have described my invention as used in connection with air, it is obvious that it may be advantageously employed in the handling of various liquids.

What is claimed is:

1. In an axial flow fan having an inner cylinder and an outer cylinder, the combination with 'said inner cylinder, of a hollow tailpiece supported by said inner cylinder and arranged on the downstream end of the cylinder, said tailpiece compris-l ing a plurality of frustro-conically-shaped members converging inwardly toward the downstream side thereof and formed at the downstream `end of the blade will cause additional air to be aS,- 75 with a central inlet opening,l and. said members being spaced from each other and having their adjacent ends in overlapping arrangement to provide aspirating openings in communication with the central inlet opening thereof.

2. An axial ow fan comprising an outer cylinder, an inner cylinder therein defining therewith an airflow passage, and a tailpiece supported by said inner cylinder on the downstream end thereof and tapering in a downstream direction, said tailpiece having an axial inlet opening in the smaller downstream end thereof for receiving air thereinto from the air pocket created beyond or at the smaller end of the tailpiece, said tailpiece being composed of a plurality of frustro-conicallyshaped members progressively decreasing in size and arranged in nested relationship with their downstream ends each overlapping the larger upstream end of the next adjacent downstream member to provide aspirating openings for emitting air by eduction of the airflow through the passage and over the tapered tailpiece, whereby the ow of air within the tailpiece is self-energized.

ALBERT E. CRIQUI.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number Name Date Stalker Nov. 20, 1928 Stalker May 26, 1936 Stalker June 22, 1937 Kurth et al Apr. l1, 1939 Honerkamp July 23, 1940 Troller Sept. 1, 1942 Chitz Mar. 23, 1943 Funk Mar. 231, 1943 FOREIGN PATENTS Country Date Great Britain Apr. 2l, 1939 

